The individual avatar service settings forms are now rendered with

prefixes so that their fields do not clobber eachother. In addition, the

rendering of forms has been drastically simplified by initializing all

forms in __init__() instead of get_extra_context() and providing the

form data there. The client-side JS has been updated to reference these

new prefixed for fields.
Also, some bugs were fixed relating to avatar services. Namely:

- we were not passing the avatar settings manager from the registry to

  each avatar service; and

- the file upload avatar service did not ever successfully validate.

Ran unit tests.
Able to change avatar services.